U.S. patent number 4,273,188 [Application Number 06/145,368] was granted by the patent office on 1981-06-16 for in situ combustion process for the recovery of liquid carbonaceous fuels from subterranean formations.
This patent grant is currently assigned to Gulf Research & Development Company. Invention is credited to Ajay M. Madgavkar, Harold E. Swift, Roger F. Vogel.
United States Patent |
4,273,188 |
Vogel , et al. |
* June 16, 1981 |
**Please see images for:
( Certificate of Correction ) ** |
In situ combustion process for the recovery of liquid carbonaceous
fuels from subterranean formations
Abstract
An integrated in situ combustion process for recovering
subterranean liquid and solid carbonaceous deposits in which the
resulting flue gas of low heating value is combusted at
substoichiometric conditions over two different oxidation catalysts
in two combustion zones in series and is expanded in a gas turbine
which drives the air compressor for injecting the combustion air
into the underground carbonaceous deposit. One of the oxidation
catalysts comprising platinum and at least one metal cocatalyst
selected from Groups IIA and VIIB, Group VIII up through atomic No.
45, the lanthanides, chromium, zinc, silver, tin and antimony is
provided to reduce the carbon monoxide in the combusted flue
gas.
Inventors: |
Vogel; Roger F. (Butler,
PA), Madgavkar; Ajay M. (Pittsburgh, PA), Swift; Harold
E. (Gibsonia, PA) |
Assignee: |
Gulf Research & Development
Company (Pittsburgh, PA)
|
[*] Notice: |
The portion of the term of this patent
subsequent to February 5, 1997 has been disclaimed. |
Family
ID: |
22512789 |
Appl.
No.: |
06/145,368 |
Filed: |
April 30, 1980 |
Current U.S.
Class: |
166/256;
166/267 |
Current CPC
Class: |
E21B
43/34 (20130101); E21B 43/243 (20130101) |
Current International
Class: |
E21B
43/16 (20060101); E21B 43/243 (20060101); E21B
43/34 (20060101); E21B 043/24 () |
Field of
Search: |
;166/256-262,302,303,251,267 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Novosad; Stephen J.
Assistant Examiner: Suchfield; George A.
Attorney, Agent or Firm: Keith; Deane E. Stine; Forrest D.
Rose; Donald L.
Claims
We claim:
1. The in situ combustion process for recovering liquid
hydrocarbons from subterranean formations which comprises injecting
a stream of combustion air into at least one injection well leading
to a combustion zone in said subterranean formation, producing
liquid hydrocarbons and combustion gas from at least one production
well, separating the liquid hydrocarbons from the stream of
combustion gas whereby a separated stream of flue gas is obtained
having a heating value between about 15 Btu/scf. and about 200
Btu/scf. and containing at least one aliphatic hydrocarbon having
from one to about seven carbon atoms, passing said flue gas stream
admixed with air for combustion through two combustion zones in
series comprising a first combustion zone and a second combustion
zone in contact with two different catalysts consisting of a
supported bimetallic catalyst comprising platinum and at least one
metal oxide cocatalyst selected from Groups IIA and VIIB, Group
VIII up through atomic No. 45, the lanthanides, chronium, zinc,
silver, tin and antimony in one combustion zone and an oxidation
catalyst which does not have the carbon monoxide suppressing
capability of the bimetallic catalyst in the other combustion zone
at a temperature in each combustion zone which is high enough to
initiate and maintain combustion of said gas stream, the total
amount of combustion air being sufficient to provide an air
equivalence ratio between about 0.20 and less than 1.0, expanding
the gas stream in a gas turbine following said catalyzed
combustion; and driving an air compressor with said gas turbine to
compress and inject said stream of combustion air into the said
subterranean combustion zone.
2. The in situ combustion process for recovering liquid
hydrocarbons from subterranean formations in accordance with claim
1 in which methane comprises at least about 50 mol percent of the
hydrocarbon component of said flue gas stream.
3. The in situ combustion process for recovering liquid
hydrocarbons from subterranean formations in accordance with claim
1 in which the heating value of the flue gas is between about 40
and about 150 But/scf.
4. The in situ combustion process for recovering liquid
hydrocarbons from subterranean formations in accordance with claim
1 in which the said bimetallic catalyst is in the first combustion
zone and the said oxidation catalyst is in the second combustion
zone.
5. The in situ combustion process for recovering liquid
hydrocarbons from subterranean formations in accordance with claim
1 in which the said oxidation catalyst is in the first combustion
zone and the said bimetallic catalyst is in the second combustion
zone.
6. The in situ combustion process for recovering liquid
hydrocarbons from subterranean formations in accordance with claims
4 or 5 in which the oxidation catalyst is a monometallic platinum
oxidation catalyst.
7. The in situ combustion process for recovering liquid
hydrocarbons from subterranean formations in accordance with claim
1 in which the heating value of the flue gas varies with time
within the said range of heating value and the amount of air for
combustion is substantially constant with time.
8. The in situ combustion process for recovering liquid
hydrocarbons from subterranean formations in accordance with claim
6 in which the variation in heating value of the flue gas in
combination with the substantially constant air feed rate does not
result in a stoichiometric excess of oxygen over a substantial
period of time.
9. The in situ combustion process for recovering liquid
hydrocarbons from subterranean formations in accordance with claim
1 in which the heating value of said flue gas is less than about 40
Btu/scf. and supplemental fuel is injected into said flue gas to
bring the heating value up to about 40 Btu/scf.
10. The in situ combustion process for recovering liquid
hydrocarbons from subterranean formations in accordance with claim
1 in which the total quantity of air for combustion of the flue gas
is fed to the flue gas stream at a rate to maintain a substantially
constant temperature in the said catalytically combusted flue gas
stream for expansion in said gas turbine.
11. The in situ combustion process for recovering liquid
hydrocarbons from subterranean formations in accordance with claim
1 in which the heating value of said flue gas is between about 50
and about 100 Btu/scf.
12. The in situ combustion process for recovering liquid
hydrocarbons from subterranean formations in accordance with claim
1 in which the cocatalyst is selected from antimony, nickel,
calcium, cobalt and tin.
13. The in situ combustion process for recovering liquid
hydrocarbons from subterranean formations in accordance with claim
1 in which the air equivalence ratio is between about 0.40 and
about 0.90.
14. The in situ combustion process for recovering liquid
hydrocarbons from subterranean formations in accordance with claim
1 in which the pressure of said combusted gas stream is at least
about 75 psi.
15. The in situ combustion process for recovering liquid
hydrocarbons from subterranean formations in accordance with claim
1 in which the temperature of the combusted flue gas fed to the gas
turbine is between about 1,200.degree. and about 2,000.degree.
F.
16. The in situ combustion process for recovering liquid
hydrocarbons from subterranean formations in accordance with claim
1 in which the temperature of the combusted flue gas fed to the gas
turbine is between about 1,400.degree. and about 1,800.degree.
F.
17. The in situ combustion process for recovering liquid
hydrocarbons from subterranean formations in accordance with claim
1 in which a stream of cooling air is injected into said combusted
flue gas to reduce the gas temperature fed to the turbine.
18. The in situ combustion process for recovering liquid
hydrocarbons from subterranean formations in accordance with claim
1 in which the said stream of flue gas is passed through the two
said combustion zones in series with a maximum of two-thirds of
said air for combustion being added to the gas stream prior to one
combustion zone and the remainder of said combustion air being
added prior to the other combustion zone.
19. The in situ combustion process for recovering liquid
hydrocarbons from subterranean formations in accordance with claim
1 in which about one-half of the air for combustion is added for
use in each combustion zone.
Description
SUMMARY OF THE INVENTION
This invention relates to the recovery of liquid carbonaceous fuel
components from subterranean formations by an in situ combustion
process in which the low heating value waste gas stream resulting
from the subterranean combustion is itself combusted aboveground.
This combusted waste gas stream is preferably utilized to power a
turbine-compressor unit which compresses the air for injection into
the formation for the in situ combustion. More particularly, this
invention relates to the substoichiometric combustion of the waste
gas stream in the presence of a catalyst which causes a substantial
reduction in the carbon monoxide content of the combusted waste gas
stream.
DETAILED DESCRIPTION OF THE INVENTION
Various carbonaceous materials occur in underground deposits in
substantial quantities but are resistive to recovery for
aboveground use. This includes viscous oils, the oil remaining in
petroleum deposits after primary or secondary production of the oil
bearing formation, shale oil occurring in solid bituminous
deposits, tar sands, coal seams too deep or too thin to mine, and
the like. It has been proposed that these fuel materials be
recovered by an in situ combustion process and some limited
attempts have been made to accomplish this. The in situ recovery of
underground fuel values involves the injection of air into the
carbonaceous deposit to burn a minor portion of the deposit in
order to produce a further portion of the deposit for use
aboveground as a liquid and/or gas. Such recovery procedures
generally result in a gas stream of low heating value, particularly
in those operations which produce a liquid hydrocarbon as the
desired product. As used herein, the expressions heating value and
heat content both refer to the energy obtainable by burning the
combustible components in the stream of waste gas.
The obvious way to handle a waste gas stream of low heat content is
to discard it directly into the atmosphere. But in recent years a
greater recognition and concern about atmospheric pollution has led
to legal standards in many areas controlling the direct emission to
the atmosphere of waste gases containing significant amounts of
hydrocarbon and carbon monoxide. Furthermore, there is a growing
recognition and concern regarding the social as well as economic
loss in wasting energy. Although these waste gas streams resulting
from in situ combustion may have a low heating value on a unit
volume analysis, they do contain a very large heating value overall
because of the enormous volumes of gas involved. It has therefore
become most desirable and even necessary that the heat content of
these waste gas streams be utilized and that the atmosphere be
spared contamination.
The combustible components in a waste gas stream from an in situ
combustion process can be burned using a suitable oxidation
catalyst. This hot gas can then be used to drive the
turbine-compressor unit which injects the required large volumes of
air at high pressure into the underground carbonaceous deposit
undergoing in situ combustion. In order to obtain the full heating
value of this waste gas as well as to avoid the emission of
undesirable components into the atmosphere, these waste gas streams
can be burned to substantially stoichiometric completion in the
presence of an oxidation catalyst. But these stoichiometrically
combusted waste gas streams generally vary in temperature over
relatively short periods of time due to inherent variations in the
heating value of these waste gas streams. In an effort to protect
the gas turbine against damage resulting from these temperature
fluctuations and to operate at the turbine's design temperature,
the combustion process involves auxiliary temperature control such
as is accomplished by the injection of supplemental fuel into the
waste gas during heating value minimums and the injection of
cooling air into the combusted waste gas during heating value peaks
to provide a constant gas temperature.
We have determined that a waste gas stream of low heat content
which varies with time can be effectively combusted at a
substantially constant combustion temperature for use in a gas
turbine. This is accomplished by combusting the gas with a constant
amount of air which is substantially less than the amount of air
required for stoichiometric combustion. Furthermore, if the heat
content of the waste gas is relatively constant but so high that
its stoichiometric combustion results in a gas temperature too high
for use in a gas turbine, its combustion temperature can be
effectively restricted to the design limits of the gas turbine by
operating at substantial substoichiometric conditions with a
constant quantity of combustion air. We have further discovered
that this substoichiometric combustion can be carried out using a
particular catalyst for the production of reduced and acceptable
carbon monoxide levels.
In carrying out a hydrocarbon recovery operation by in situ
combustion such as in a tertiary recovery process in a partially
depleted oil field, combustion air is pumped at a substantial
pressure through an injection well into the combustion zone. By a
combination of heating and cracking the oil is liquefied and caused
to flow to one or more production wells. The hot, substantially
oxygen-free gas stream, after passage through the combustion zone
is cooled down to the reservoir temperature by the time it arrives
at the production well. As it is produced, it contains significant
quantities of entrained liquid hydrocarbons as well as gaseous
hydrocarbons and minor amounts of carbon monoxide, hydrogen and
hydrogen sulfide. The liquid hydrocarbons are removed from the gas
stream in an aboveground separator. The combustible component of
the waste gas stream leaving the separator is principally methane
but it also contains minor amounts of other hydrocarbons having up
to about five carbon atoms and in some instances up to about seven
carbon atoms, as well as the carbon monoxide, hydrogen and hydrogen
sulfide. The remainder is principally nitrogen and carbon
dioxide.
The combustible components in this waste gas stream can be mixed
with a stoichiometric excess of air and burned in the presence of a
suitable oxidation catalyst such as platinum if it is at its
ignition, or light off, temperature, which varies with the gas
composition and the nature of the oxidation catalyst. If the
catalyst is provided in a suitable physical form to provide
adequate contact of the large volume of gas with the catalyst,
substantially complete combustion of the hydrocarbon to carbon
dioxide and water is accomplished. This combusted gas stream, at an
elevated pressure, can be directed to the turbine-compressor unit
for compressing the combustion air which is injected into the
undergound combustion zone.
But, unfortunately the waste gas stream generally varies in heating
value over a period of time, even from hour to hour, as a result of
inherent variations in the underground formation and the combustion
process. As a result, the temperature of the combusted waste gas
stream will vary in temperature with complete combustion. Since gas
turbines are designed for constant temperature operation,
adjustments must be made to control the temperature of the
combusted gas stream so that it can be utilized in a gas
turbine.
We have discovered that an in situ combustion process can be
successfully carried out in a subterranean hydrocarbon deposit by
an integrated operation in which the heat energy in the combusted
waste gas directly powers a turbine driven air compressor even
though the heating value of the waste gas stream varies with time.
Even though the waste gas stream varies in heating value, we obtain
a constant combustion temperature by using a constant
substoichiometric amount of air for the combustion which is also
sufficient to provide the desired turbine operating temperature. As
a result of this substoichiometric combustion, the combusted waste
gas stream will still have a variable but generally minimal heating
value. The heating value in the compressor exhaust gas, if
significant, can be recovered by a further catalytic combustion and
utilized to produce steam or heated water as may be needed on the
recovery site. Or the turbine exhaust can be directly vented to the
atmosphere. We have further discovered that the carbon monoxide
content of the turbine exhaust can be restricted to acceptable
amounts, notwithstanding the substoichiometric combustion, if the
waste gas is combusted in the presence of a multicomponent
oxidation catalyst as described herein.
The substoichiometric combustion of the low heating value waste gas
stream is carried out by our process using an air equivalence
ratio, or A.E.R., of less than 1.0, generally of at least about
0.20 up to about 0.90 (the denominator of this ratio being 1.0 is
not expressed), and more generally an air equivalence ratio of at
least about 0.4 and a maximum of about 0.80. As used herein, air
equivalence ratio is the ratio of the amount of air actually used
in the partial combustion process to the amount of air required at
the same conditions of pressure and temperature for stoichiometric
combustion of all combustible components in the gas stream.
In our study of the platinum-catalyzed, substoichiometric
combustion of a dilute hydrocarbon stream we made several
interesting observations. First, it was found that the only
combustibles present in this partially combusted gas stream are
carbon monoxide, hydrogen and unreacted hydrocarbon. Second, we
observed that in this partial combustion the amount of carbon
monoxide reached a maximum at an air equivalence ratio of about
0.6. In fact, we found that the amount of carbon monoxide
substantially exceeded the amount of carbon dioxide in the
combusted gas at an A.E.R. of 0.6, such that the ratio of carbon
dioxide to carbon monoxide was less than 1.0 at an A.E.R. between
about 0.4 and about 0.7.
As would be expected in the platinum-catalyzed reaction, the molar
ratio of carbon dioxide to carbon monoxide rapidly increased as the
A.E.R. approached 1.0. But surprisingly, we discovered that the
molar ratio of carbon dioxide to carbon monoxide also rapidly
increased as the A.E.R. was reduced to values less than about 0.4.
This is surprising because it is not consistent with the
conventional teaching that carbon monoxide is the result of
incomplete combustion of a hydrocarbon. If this conventional
teaching were applied to this particular combustion system, the
ratio of carbon monoxide to carbon dioxide would be expected to
increase as the air equivalence ratio decreased, and that it would
be expected to be particularly large at small air equivalence
ratios. We conclude from our combustion tudies that the carbon
monoxide in this platinum-catalyzed, substoichiometric combustion
of a dilute hydrocarbon is primarily the result of secondary
reactions including the steam reforming and water gas shift
reactions.
In the steam reforming reaction, hydrocarbons such as methane and
water are in equilibrium with carbon monoxide and hydrogen. In the
water gas shift reaction carbon monoxide and water are in
equilibrium with carbon dioxide and hydrogen. Thus, a study of
these equilibrium reactions suggests several mechanisms for the
unexpected product mixture of the oxides of carbon including the
substantial production of carbon monoxide and a corresponding
minimum in the carbon dioxide to carbon monoxide ratio at an air
equivalence ratio of about 0.6.
When methane is the primary combustible component in the waste gas
stream, it will be substantially the only hydrocarbon in the gas
exhausted to the atmosphere which is fortuitous since methane, in
limited amounts, is not considered to be a pollutant in the
atmosphere. It can be shown that a mixture of diluted, gaseous,
paraffinic hydrocarbons will react at different rates when burned
in a deficiency of air. The higher paraffinic hydrocarbons burn
readily, while the lower the number of carbon atoms in the
molecular structure the more resistant to combustion is the
hydrocarbon. As a demonstration of this variable combustibility, a
nitrogen-diluted two weight percent mixture of one to five carbon
paraffinic hydrocarbons was burned in a combustion furnace with
fifty percent of the stoichiometric amount of air for complete
combustion. The gas, heated to 840.degree. F. and passed in contact
with a supported platinum oxidation catalyst, reached a maximum
temperature of 1430.degree. F. In this combustion experiment 100
percent of the n-pentane was converted, 54.5 percent of the
n-butane, 44.1 percent of the propane, 31.8 percent of the ethane
and 11 percent of the methane. This demonstrates that partial
combustion of a dilute gaseous hydrocarbon mixture including
methane will substantially increase the proportion of methane in
the produce gas.
The temperature of the waste gas stream will only be moderately
higher than ambient temperature due to the cooling effect of the
formation following the underground combustion. Therefore, it is
necessary to preheat the waste gas stream for catalytic combusion,
preferably after the air for combustion has been injected into the
waste gas stream. This preheating must be at least as high as the
ignition, or light off, temperature of the gas. The preferred means
for preheating the waste gas stream is by heat exchange with the
hot combusted gas stream leaving the combustion zone. In general,
two combustion chambers in series are preferred in order to avoid
an excessive temperature rise in a single combustion chamber. In
this two-stage combustion process, the waste gas stream is
desirably preheated after the first combustion stage. The
temperature of the combusted gas stream is dependent on a number of
factors including the heating value of the waste gas stream, the
temperature of the waste gas stream prior to preheating, the amount
of air that is used for combustion, the inherent heat losses in the
system, and the like.
With regard to the many conditions and variables which may be
involved in any specific in situ combustion operation, the waste
gas streams which are combusted to temperatures that are useful in
gas turbines desirably have a heat content of at least about 40
Btu/scf., preferably about 50 Btu/scf., however, heating values as
low as 15 to 25 Btu/scf. can be utilized under appropriate
conditions including the injection of supplemental fuel. The
maximum heating value of the waste gas stream obtained by the in
situ combustion procedure will be about 200, more generally a
maximum of about 150 and most likely a maximum heating value of
about 100 Btu/scf.
A supported platinum catalyst is in general preferred as an
oxidation catalyst because platinum is both a highly active
oxidation catalyst and is also relatively sulfur tolerant. However,
the use of platinum in substoichiometric combustion tends to result
in relatively high carbon monoxide levels in the combusted gas.
Other metals, or suitable mixtures or combinations of metals, such
as ruthenium, palladium, rhodium, osmium, iridium, vanadium,
cobalt, nickel, iron, copper, manganese, chromium, molybdenum,
titanium, silver, cerium and the like, can be used as oxidation
catalysts, but are generally less desirable for oxidation than a
platinum catalyst.
In accordance with our invention the carbon monoxide content
resulting from the substoichiometric combustion of a flue gas is
suppressed by the use in the substoichiometric combustion of a
platinum and cocatalyst combination of the type described in our
U.S. Pat. No. 4,186,801. In the more effective catalyst
combination, herein designated the bimetallic catalyst, the carbon
monoxide level in the substoichiometric combustion of low heating
value flue gas streams can be substantially reduced by the use of a
cocatalyst selected from Groups IIA and VIIB, Group VIII up through
atomic No. 45, the lanthanides, chromium, zinc, silver, tin, and
antimony with the platinum oxidation catalyst. The metals in these
names groups which are particularly useful as a cocatalyst with
platinum are magnesium, calcium, manganese, iron, cobalt, nickel,
ruthenium, rhodium, cerium, and mixed lanthanides containing
cerium.
The oxidation catalyst that is used in our substoichiometric
combustion process is desirably carried on an inert support. Since
the catalytic combustion inherently involves a relatively large
volume of the stream of low heating value gas, the support is
preferably of a design to permit good solid-gas contact at
relatively low pressure drop. A suitable support can be formed as a
monolith with hexagonal cells in a honeycomb design. Other cellular
relatively open-celled designs are also suitable.
The support for the catalysts to be used in the process of this
invention can be any of the refractory oxide supports well known in
the art, such as those prepared from alumina, silica, magnesia,
thoria, titania, zirconia, silica-aluminas, silica-zirconias,
magnesia-aluminas, and the like. Other suitable supports include
the naturally occurring clays, such as diatomaceous earth.
Additional desirable supports for use herein are the more recently
developed corrugated ceramic materials made, for example, from
alumina, silica, magnesia, and the like. An example of such
material is described in U.S. Pat. No. 3,255,027 and is sold by E.
I. duPont de Nemours & Company as Torvex. More recently,
metallic monoliths have been fabricated as catalyst supports and
these may be used to mount the catalytic material. An example of
these supports is Fecralloy manufactured by Matthey Bishop, Inc.
under U.S. Pat Nos. 3,298,826 and 3,920,583.
If desired, the catalyst and cocatalyst, if used, can be mounted
directly onto the surface of the monolith. Or the monolith can
first be coated with refractory oxide, such as defined above, prior
to the deposition of these materials. The addition of the
refractory oxide coating allows the catalyst to be more securely
bound to the monolith and also aids in its dispersion on the
support. These coated monoliths possess the advantage of being
easily formed in one piece with a configuration suitable to permit
the passage of the combustion gases with little pressure drop. The
surface area of the monolith generally is less than one square
meter per gram. However, the coating generally has a surface area
of between about ten and about 300 m.sup.2 /g. Since the coating is
generally about ten percent of the coated support, the surface area
of the coated support will therefore generally be between about one
and about 30 m.sup.2 /g.
In preparing the platinum and cocatalyst combination it is
preferred that the cocatalyst be placed on the support before the
platinum. However, the reverse order of emplacement is also
suitable or the platinum and cocatalyst can be added in a single
step. In the preferred procedure a suitable salt of the cocatalyst
metal is dissolved in a solvent, preferably water. The support is
impregnated with the solution of the cocatalyst metal. In a
preferred embodiment the impregnated support is next gassed with a
suitable gas, generally ammonia or hydrogen sulfide, to cause the
catalyst metal to precipitate uniformly on the support as the
hydroxide or sulfide as the case may be. It is then dried and
calcined in air at about 800.degree. to 1200.degree. F., preferably
at about 1000.degree. F. Hydrogen may be used to reduce the
cocatalyst compound to the metal if desired.
Platinum is impregnated onto the support, either alone or in
association with a cocatalyst as an aqueous solution of a
water-soluble compound such as chloroplatinic acid, ammonium
chloroplatinate, platinum tetramine dinitrate, and the like. The
catalyst is then gassed with hydrogen sulfide in a preferred
embodiment to cause precipitation of the platinum as the sulfide to
ensure uniform distribution of the platinum on the support. It is
again dried and then calcined in air at about 800.degree. to
1200.degree. F., preferably at about 1000.degree. F. The same
general procedure can be used for the incorporation of a different
oxidation catalyst on the support. In general, it is not certain
whether calcination converts the catalyst metal sulfides and
hydrated sulfides to another compound or how much is converted to
the oxide, sulfite or sulfate, or the metal itself. Nevertheless,
for convenience, the noble metals such as platinum are reported as
the metal and the other catalyst metals are reported as the
oxide.
The catalyst can also be added to the coated monolith as a slurry
of finely ground powders. In the case of the noble metals such as
platinum, powdered metal is preferred but the platinum could also
be added as the powdered oxide. The other catalyst metals would
preferably be added as the powdered oxide or sulfide. The powdered
metals could be added together or in succession with calcining as
described above. In a further alternative the coating material such
as powdered alumina is impregnated with a solution of the metal
compound and calcined. The monolith is then coated with a slurry of
this powder and calcined. In this latter technique all of the
catalyst components can be added to the monolith in one step.
The supported catalyst is prepared so that it contains between
about 0.005 and about 20 weight percent of the catalyst metal
reported as the oxide, and preferably between about 0.1 and about
15 weight percent of the metal oxide. The platinum or other noble
metal is used in an amount to form a finished supported catalyst
containing between about 0.005 and about ten weight percent of the
metal, and preferably about between 0.01 and about seven weight
percent of the metal. When the platinum and cocatalyst combination
is used for lowered carbon monoxide content in the product gas
stream, the relative amount of the cocatalyst and the platinum has
an effect on the combustion, including an effect in the amount of
carbon monoxide in the combusted gas. The catalyst will broadly
contain a mol ratio of cocatalyst as the oxide to platinum as the
metal of between about 0.01:1 and about 200:1, preferably between
about 0.1:1 and about 100:1, and most preferably between about
0.5:1 and about 50:1.
DESCRIPTION OF PREFERRED EMBODIMENTS
The reactor used in the following experiments, at atmospheric
pressure was a one-inch I.D. forged steel unit which was heavily
insulated to give adiabatic reaction conditions. The reactor used
in the combustion under pressure was made from Incoloy 800 alloy
(32 percent Ni, 46 percent Fe and 20.5 percent Cr) but was
otherwise the same. The catalyst consisted of three one-inch
monoliths wrapped in a thin sheet of a refractory material
(Fiberfrax, available from Carborundum Co.). The catalyst
compositions, as specified, are only approximate because they are
based on the composition of the impregnating solution and the
amount absorbed and are not based on a complete chemical analysis
of the finished catalyst. Well insulated preheaters were used to
heat the gas stream before it was introduced into the reactor. The
temperatures were measured directly before and after the catalyst
bed to provide the inlet and outlet temperatures. An appropriate
flow of preheated nitrogen and air was passed over the catalyst
until the desired feed temperature was obtained.
Preheated hydrocarbon was then introduced at a gas hourly space
velocity of 42,000 per hour on an air-free basis and combustion was
allowed to proceed until steady state conditions were reached. The
feed gas stream contained 94.5 mol percent nitrogen, 3.75 mol
percent methane, 0.98 mol percent ethane, 0.77 percent propane and
400 ppm. hydrogen sulfide, except otherwise noted. The heating
value of this feed stream is about 75 Btu/scf. The experiments were
conducted at atmospheric pressure or at a slightly elevated
pressure, except where otherwise noted. The analyses were made
after steady state conditions were reached on a water-free basis.
The conversion is the overall conversion of all hydrocarbon
constituents. No measurable free oxygen occurred in the product gas
stream .
EXAMPLE 1
The preparation of a catalyst containing antimony as the cocatalyst
is now described. A Torvex monolith was used as the support. The
Torvex support, a product of E. I. duPont de Nemours and Company
was a mullite ceramic in the shape of a honeycomb having a coating
of alumina of about 25 m.sup.2 /g. surface area. The support was
cut into one inch diameter by one inch deep pieces and freed from
dust. This support material was impregnated with a solution
containing 15.96 g. of antimony trichloride in 44.04 g. of a 1:3
solution of HCl and water by soaking for 15 minutes. These pieces
of support was drained of excess solution and treated with gaseous
ammonia for 30 minutes to precipitate the antimony as the
hydroxide. The support material was then dried at 120.degree. C.
and calcined at 1000.degree. F.
The pieces were next soaked for 15 minutes in an aqueous solution
of chloroplatinic acid containing 23 mg. of platinum per ml. After
removing excess solution from the support material, it was gassed
with hydrogen sulfide for 30 minutes to precipitate the platinum as
platinum sulfide. The catalyst was then dried at 120.degree. C. and
calcined at 1000.degree. F.
Other catalysts were prepared in an identical manner except that
where necessary the cocatalyst was precipitated with hydrogen
sulfide instead of with ammonia such as a catalyst prepared by
impregnating the support with an aqueous solution of nickel
nitrate.
EXAMPLE 2
A catalyst was made as described in Example 1 containing about 0.3
percent platinum but the cocatalyst was omitted for comparison
purposes. The operating data, including the inlet and outlet gas
temperatures, and results for a number of combustion runs over a
series of air equivalence ratios are set out in Table I.
TABLE I ______________________________________ Temperature,
.degree.F. CO CO.sub.2 Run AER Inlet Outlet Mol % Mol % Conv. %
______________________________________ 1.sup.a 0.2 700 943 0.14
1.28 19.3 2 0.3 650 1062 0.45 1.66 23.3 3 0.4 650 1148 1.17 1.69
42.1 4.sup.a 0.5 650 1236 1.94 1.66 57.3 5 0.6 650 1315 2.42 1.79
71.4 6.sup.a 0.7 650 1415 2.11 2.43 81.5 7 0.8 650 1596 0.75 4.03
-- ______________________________________ .sup.a Average of 2 runs
on different days.
A study of Table I discloses that over a wide range of air
equivalence ratios the amount of carbon dioxide remains relatively
constant between an A.E.R. of about 0.3 to about 0.6 while the
amount of carbon monoxide rapidly increases in this range to an
unexpected peak at an A.E.R. of about 0.6. Over this range of
increasing oxygen, the conversion and overall amount of carbon
oxides increase, as would be expected. It is further noted that the
largest carbon dioxide to carbon monoxide ratio surprisingly occurs
at minimum oxygen, such as illustrated at an A.E.R. of 0.2, since
the production of carbon monoxide unexpectedly decreases much more
than the production of carbon dioxide as the amount of oxygen
decreases in the low range of air equivalence ratios.
That the maximum carbon dioxide to carbon monoxide ratio occurs at
minimum oxygen strongly suggests to us that the principal source of
carbon monoxide in the system is not from incomplete combustion,
that is, the direct but partial oxidation of the hydrocarbon to
carbon monoxide and water. If this reaction were the principal
source of the carbon monoxide, then the minimum carbon dioxide to
carbon monoxide ratio would be expected to occur at minimum oxygen.
Instead of surprising occurrence of maximum carbon monoxide and
minimum carbon dioxide ratio in the mid A.E.R. range, strongly
suggests that another mechanism is the primary source of the carbon
monoxide, such as the steam reforming reaction and the water gas
shift reaction.
EXAMPLE 3
A catalyst was made as described in Example 1 containing tin
calculated as about 1.0 percent tin oxide, SnO.sub.2, and about 0.3
percent platinum. The operating data and results over a series of
air equivalence ratios are set out in Table II.
TABLE II ______________________________________ Temperature,
.degree.F. CO CO.sub.2 Run AER Inlet Outlet Mol % Mol % Conv. %
______________________________________ 8 0.2 745 1069 0.06 1.35
19.9 9 0.3 649 1170 0.14 1.89 27.8 10 0.4 649 1297 0.37 2.19 37.5
11 0.5 649 1413 0.63 2.49 44.8 12 0.6 649 1519 0.79 2.79 56.2
13.sup.a 0.7 649 1619 1.08 3.12 70.5 14.sup.a 0.8 650 1786 0.86
3.86 91.3 ______________________________________ .sup.a Average of
2 runs on different days.
EXAMPLE 4
A series of catalysts were prepared by the two-stage procedure used
in Example 1 and tested to illustrate the effect of the cocatalyst
combination in carbon monoxide reduction. Many of these catalysts
were tested at different air equivalence ratios and it was found
that the maximum carbon monoxide occurred at an A.E.R. of about 0.7
when a cocatalyst was used with platinum. This contrasts with
maximum carbon monoxide occurring at an A.E.R. of 0.6 when no
cocatalyst is used with platinum.
Table III summarizes a series of experiments by setting forth the
results of various catalytic combinations at an A.E.R of 0.7 for
the two-component catalysts, and an A.E.R. of 0.6 for the
platinum-only catalysts. All runs were carried out at an inlet
temperature of 649.degree.-650.degree. F. The catalysts contained
approximately 0.3 weight percent platinum, except where specially
noted.
TABLE III ______________________________________ Out- CO CO.sub.2
Run Cocatalyst let, .degree.F. Mol % Mol % Conv. %
______________________________________ 15.sup.a -- 1285 2.85 1.59
76.3 5 -- 1315 2.42 1.79 71.4 16.sup.b 0.7%Fe.sub.2 O.sub.3 1599
1.15 3.00 70.5 17.sup.b 0.5%SnO.sub.2 1607 1.12 3.18 72.4 18 1%CoO
1625 0.85 3.09 72.0 19 1%CaO 1642 0.83 2.96 67.6 20.sup.b
3%SnO.sub.2 1616 0.68 3.32 69.2 21 1%NiO 1652 0.48 3.34 68.2 22
1%Sb.sub.2 O.sub.3 1684 0.46 3.40 65.8
______________________________________ .sup.a 0.5% platinum. .sup.b
Average of 2 runs on different days.
EXAMPLE 5
Data for a further series of bimetallic catalysts that were
unsuccessfully tested at an air equivalence ratio of 0.7 are set
out in Table IV. All of the catalysts contained approximately 0.3
weight percent platinum except where indicated otherwise.
TABLE IV ______________________________________ Run Cocatalyst Pt
Inlet Temp. .degree.F. Conv. %
______________________________________ 23.sup.a CuO 0.3% 770 --
24.sup.a 1%Bi.sub.2 O.sub.3 0.3% 770 -- 25.sup.a 1%V.sub.2 O.sub.5
0.3% 732 -- 26.sup.a 0.3%CuO+ 0.3%Cr.sub.2 O.sub.3 0.3% 750 --
27.sup.b 0.3%CuO+ 0.3%Cr.sub.2 O.sub.3 none 650 -- 28.sup.b 1%PbO
0.3% 649 -- ______________________________________ .sup.a Unstable
combustion, steady state combustion never reached. .sup.b No
combustion.
The data in this table show that some metals that are known to be
effective oxidation catalysts are not effective as cocatalysts with
platinum in the present substoichiometric process. For example,
copper oxide, vanadium oxide, lead oxide and copper chromite are
recognized as oxidation catalysts. In contrast, tin oxide which is
shown in Table III to be an effective suppressor of carbon monoxide
with a platinum oxidation catalyst in substoichiometric combustion,
is not itself effective as an oxidation catalyst.
EXAMPLE 6
In this experiment a different low heating value gas stream
containing higher hydrocarbons and carbon monoxide was used. It
contained 5.5 volume percent of a hydrocarbon-carbon monoxide
mixture which comprised 67.89 mol percent methane, 7.76 percent
ethane, 5.83 percent propane, 7.73 percent n-butane, 5.04 percent
n-pentane, 0.96 percent n-hexane and 4.79 percent carbon monoxide.
The remainder was nitrogen and 400 ppm. hydrogen sulfide. The
catalyst, containing about 0.5 percent platinum on an
alumina-coated Torvex support, was the same as the catalyst used in
Run 15. The operating data over a series of air equivalence ratios
are set out in Table V.
TABLE V ______________________________________ Temperature,
.degree.F. CO CO.sub.2 Run AER Inlet Outlet Mol % Mol % Conv. %
______________________________________ 29 0.2 650 925 0.10 1.56
18.3 30 0.3 650 1047 0.68 1.86 25.9 31 0.4 650 1150 1.76 1.64 36.9
32 0.5 650 1234 3.20 1.23 59.2 33.sup.a 0.6 650 1318 3.64 1.57 81.3
34 0.7 650 1409 3.11 2.42 85.7 35 0.8 650 1555 1.77 3.46 .about.100
______________________________________ .sup.a Average of 2 runs on
different days.?
EXAMPLE 7
Runs 36-42 were carried out under pressure using an inlet pressure
to the reactor of 90 psia. The catalyst again contained about 0.5
percent platinum on an alumina-coated Torvex support. The operating
data over a series of air equivalence ratios and gas hourly space
velocities (10.sup.-3 hr..sup.-1) are set out in Table VI.
TABLE VI ______________________________________ Temperature,
.degree.F. CO CO.sub.2 GHSV AER Inlet Outlet Mol % Mol % Conv. %
______________________________________ 20 0.4 650 1127 1.12 2.06
38.6 42 0.4 390 1146 0.52 2.41 36.3 80 0.4 500 1282 0.86 2.09 37.9
100 0.4 500 1329 0.81 2.03 36.6 15.sup.a 0.42 500 1075 0.54 2.23
40.8 100 0.5 500 1424 1.61 2.00 49.9 25.sup.b 0.61 650 1192 1.01
2.03 66.5 ______________________________________ .sup.a Gas
contained 5.27 percent hydrocarbon and 72 Btu/scf. .sup.b Gas
contained 3.7 percent hydrocarbon and 51 Btu/scf.
EXAMPLE 8
Runs 43-51 were also carried out at a pressure of 90 psia. in the
combustion reactor but using a different catalyst containing about
0.3 percent platinum and about one percent cobalt oxide. The
operating data over a series of air equivalence ratios and gas
hourly space velocities (10.sup.-3 hr..sup.-1) are set out in Table
VII.
TABLE VII ______________________________________ Temperature,
.degree.F. CO CO.sub.2 GHSV AER Inlet Outlet Mol % Mol % Conv. %
______________________________________ 42.sup.a 0.4 500 1233 0.20
2.89 35.2 100.sup.a 0.4 500 1309 0.20 2.43 33.0 42.sup.b 0.4 500
1235 0.21 2.52 33.3 80 0.4 500 1340 0.38 2.44 33.1 140.sup.c 0.4
500 1291 0.32 2.28 32.4 80 0.6 500 1532 0.68 3.03 53.9 42.sup.d 0.7
525 1446 0.60 3.67 65.4 42 0.7 650 1605 0.89 3.46 67.5 80 0.8 500
1760 1.06 3.74 72.1 ______________________________________ .sup.a
At 61 psia. .sup.b Average of 2 runs on different days. .sup.c Gas
contained 5.37% hydrocarbon and 73 Btu/scf. .sup.d Gas contained
5,000 ppm H.sub.2 S.
EXAMPLE 9
Several of the bimetallic catalysts, which resulted in the greatest
reduction in the production of carbon monoxide, as set forth in
Table III were tested to determine the minimum temperature, the
light off temperature, to which a feed gas stream must be heated to
maintain continuous combustion. The various light off temperatures
(L.O.T.) and the carbon monoxide produced under the specific
conditions of these runs are set out in Table VIII after relatively
steady state operation was apparently reached.
TABLE VIII ______________________________________ Run Pt. % Other
Metal L.O.T., .degree.F. CO, Mol %
______________________________________ 52 0.3 -- 515 1.50 53 0.3
1%CoO 535 0.72 54 0.3 1%Sb.sub.2 O.sub.3 560 0.39 55 0.3
1%SnO.sub.2 590 0.86 56 0.3 1%NiO 615 0.78 57 0.3 1%CaO 650 0.83
______________________________________
Since the light off temperature is an indicator of the relative
oxidation activity of a catalyst, the lower the light off
temperature the more active the catalyst, this data indicate that
th cocatalyst does not promote the oxidation activity of the
platinum. The data in the above examples suggests that the
cocatalyst in the bimetallic catalyst does not affect the oxidation
reaction per se, but rather that it functions in some other manner
to cause a reduction in carbon monoxide such as, for example, by
directing the steam reforming reaction and the water gas shift
reaction to reduced carbon monoxide levels.
When two combustion zones are utilized in substoichiometric
combustion, the bimetallic catalyst can be used, if desired, in
either the first or the second combustion zone and an oxidation
catalyst, such as platinum, which does not have the carbon monoxide
suppressing capability of the bimetallic catalyst can be used in
the other combustion zone for substantial overall suppression of
carbon monoxide in the combusted gas fed to the gas turbine.
The information obtained from these experiments is utilized in an
integrated tertiary oil recovery operation by in situ combustion
according to the following example.
EXAMPLE 10
An in situ fire flood is initiated in an oil zone in an undergound
petroleum reservoir at an overall depth of about 6,000 feet. Oil
production from the formation had been exhausted following
secondary recovery by water injection. The fire is initiated in the
formation and steady state conditions are reached in about 10
weeks. At this time about 9.1 million scf. per day of air at a
temperature of about 200.degree. F. and a pressure of about 3,800
psi. are pumped into the injection well by a multistage compressor,
which is driven by a gas turbine. The combusted gas and entrained
hydrocarbon liquids are produced in adjacent production wells. The
entrained liquids are removed in a separator resulting in about 7.5
million scf. per day of liquid-free, waste flue gas of low heat
content. The temperature of this flue gas is about 95.degree. F.
and its gauge pressure is about 150 psig. Its average analysis over
a 19-day period is about 2.2 percent methane, about 0.5 percent
ethane, about 0.4 percent propane, about 0.3 percent butane, about
0.25 percent pentanes, about 0.2 percent hexanes and higher, about
500 ppm. sulfur, about 15 percent carbon dioxide, about one percent
argon and the remainder nitrogen. Its average heat content for this
19-day period is about 78 Btu/scf. with a maximum value of about 91
and a minimum value of about 61 during this period.
This flue gas is combusted in two stages. The catalyst in the
second stage is a bimetallic oxidation catalyst in the first stage
is a monometallic platinum oxidation catalyst comprising about 0.3
percent platinum on an alumina-coated Torvex monolithic ceramic
support. The catalyst comprising about one percent cobalt oxide and
about 0.3 percent platinum impregnated on the same support as used
in the first stage. Over this 19-day period under study the flue
gas is combusted by the injection of a constant amount of air,
approximately equally divided between the input to each combustion
stage, to provide an average air equivalence ratio of about 0.64.
As a result the combustion is substoichiometric over the entire
19-day period. The flue gas-air mixture is heated above its
ignition temperature by heat exchange with the combusted gas from
the first stage before it is introduced into the first combustor.
The combusted flue gas is mixed with the second portion of
combustion air after the heat exchanger and prior to entering the
second combustor. The gas stream leaving the second combustor has a
temperature of about 1,550.degree. F. This hot gas stream is used
to drive the gas turbine which is designed for an operating
temperature of 1,450.degree. F. Therefore, a sufficient quantity of
the 200.degree. F. compressed air is bled from the compressed air
line and injected into the combusted flue gas prior to the turbine
inlet to drop its temperature to about 1,450.degree. F. The
combusted flue gas is introduced into the turbine at a gauge
pressure of about 90 psia. and exits at near atmospheric pressure.
Since the second combustor used the bimetallic catalyst, the
turbine exhaust contains less than one percent carbon monoxide
permitting it to be vented directly to the atmosphere.
The pressure of the air injected into subterranean deposits of
carbonaceous materials will vary over a wide range, such as about
500 psi. to about 5,000 psi or even wider. The actual pressure used
depends on many factors including the depth and down-hole pressure
in the formation, the permeability of the formation, the distance
between the injection and producing holes, and the like. In any
particular recovery operation utilizing in situ combustion the
injection pressure limits are a minimum pressure sufficient to
obtain adequate flow of gas through the formation and a maximum
pressure less than the amount which would crack the formation and
permit the air to bypass the combustion zone. There will generally
be a substantial diminution of the gas pressure between the
injection and production wells, the amount depending on the many
variables inherent in the characteristics of the formation as well
as the variables in the operating procedures. In order to
effectively carry out an integrated operation in which the flue gas
under pressure is combusted and used to drive a gas turbine, as
described herein, it is desirable that the recovered flue gas
possess a pressure of at least about 75 psi.
The air compressor can be operated at a temperature as low as about
1,200.degree. F. or even lower, but since efficiency exhibits a
significant drop at the lower temperatures, it is preferred to
operate at a temperature at which significant efficiency is
obtained, and particularly a temperature of at least about
1,400.degree. F. The maximum temperature is determined by the
temperature resistance of the materials from which the turbine is
constructed and can be about 2,000.degree. F. or even higher
particularly if the compressor is designed with provision for
auxiliary cooling but it is preferred that the maximum operating
temperature be about 1,800.degree. F. Generally, a large capacity
turbine of the type which would be used in the utilization of waste
gases from subterranean in situ combustion processes is designed
for optimum operation within a specific restricted temperature
range.
In the two-stage combustion procedure, it is desirable if at least
about one-third of the total air which is to be used in the
substoichiometric combustion be added in one combustor, and it is
generally preferred that about one-half of this combustion air be
added in each combustor. This variation in the amount of combustion
air added to each combustor permits the temperature of the waste
gas stream, entering the first stage reactor following heat
exchange with the combusted gas from the first stage, to be varied.
This air that is used for combustion of the waste gas, as well as
the air that may be used for cooling the combusted waste gas down
to the desired turbine operating temperature, needs to have a
pressure only moderately higher than the pressure of the gas
streams into which it is injected. For this reason, it is preferred
that this air be obtained from a separate low pressure compressor
or from a low pressure stage in the multistage compressor rather
than using the high pressure air that is obtained for injection
into the in situ combustion zone.
As indicated, the temperature of the gas stream following the
combustion zone cools down as it flows through the formation so
that it is about the reservoir temperature by the time it is
produced. As a result, water vapor in the gas will condense out
into the formation prior to the production wells. Additionally, it
is believed that sulfur dioxide which may be produced in the
underground combustion will remain in the reservoir with the
water.
As the final stages of the in situ combustion near, the combustion
zone approaches a production well and shows its presence by causing
a significant temperature elevation. Since some of the down-hole
gases are used to replace the hydrocarbons which are displaced in
the direction of the production wells, and since some of the gases
leak off into other formations, the amount of flue gas will be less
than the amount theoretically obtainable from the quantity of
injected air.
The subterranean formations from which liquid hydrocarbons are
obtained by the herein defined process include deposits of viscous
oils, petroleum deposits after primary or secondary production of
the oil bearing formation, oil-bearing shale occurring as solid
bituminous deposits, tar sands, coal seams too difficult or too
expensive to mine, and the like.
It it to be understood that the above disclosure is by way of
specific example and that numerous modifications and variations are
available to those of ordinary skill in the art without departing
from the true spirit and scope of the invention
* * * * *